wip: header lba

swysocki · Nov 9, 2021 · d204cd9 · d204cd9
1 parent 40e636c
commit d204cd9
Show file tree

Hide file tree

Showing 2 changed files with 25 additions and 2 deletions.
diff --git a/pygpt_disk/table.py b/pygpt_disk/table.py
@@ -14,21 +14,41 @@
 LBA 2 - 33 partitions
 """
 from pygpt_disk.disk import Disk
+import struct
 
 
 class Table:
-    _header_sig = b"\x45\x46\x49\x20\x50\x41\x52\x54"
-    _revision = b"\x00\x00\x01\x00"
+    _header_sig = b"\x45\x46\x49\x20\x50\x41\x52\x54"  # "EFI PART"
+    _revision = b"\x00\x00\x01\x00"  # "1.0"
+    _header_size = b"\x5C\x00\x00\x00"  # 92 bytes
+    _header_crc = (
+        b"\x00\x00\x00\x00"  # CRC/zlib of header with this field zero'd during calc
+    )
+    _reserved = b"\x00\x00\x00\x00"  # reserved (all zeros)
 
     def __init__(self, disk: Disk) -> None:
         self.disk = disk
+        self._primary_header_lba = int(self.disk.sector_size / self.disk.sector_size)
+        self._backup_header_lba = int(
+            (self.disk.size - self.disk.sector_size) / self.disk.sector_size
+        )
 
     def create(self) -> None:
         """Create blank GPT Table Header"""
         # move to LBA 1
         self.disk.buffer.seek(self.disk.sector_size)
         self.disk.buffer.write(Table._header_sig)
         self.disk.buffer.write(Table._revision)
+        self.disk.buffer.write(Table._header_size)
+        self.disk.buffer.write(Table._header_crc)
+        self.disk.buffer.write(Table._reserved)
+        # use struct.pack with implicit native byte order and long type to
+        # align data on 8 byte boundaries
+        self.disk.buffer.write(struct.pack("l", self._primary_header_lba))
+        self.disk.buffer.write(struct.pack("l", self._backup_header_lba))
         self.disk.buffer.seek(self.disk.size - 1)
         # move to the end of the buffer and write to avoid truncating the stream
         self.disk.buffer.write(b"\0")
+
+    def checksum_header(self) -> None:
+        pass
diff --git a/tests/test_table.py b/tests/test_table.py
@@ -14,4 +14,7 @@ def test_init(fresh_disk: disk.Disk):
     t.disk.buffer.seek(fresh_disk.sector_size)
     assert t.disk.buffer.read(8) == b"EFI PART"
     assert t.disk.buffer.read(4) == b"\x00\x00\x01\x00"
+    assert t.disk.buffer.read(4) == b"\x5C\x00\x00\x00"
+    assert t.disk.buffer.read(4) == b"\x00" * 4
+    assert t.disk.buffer.read(4) == b"\x00" * 4
     fresh_disk.write()